Single-line editing prop

[insin]

Add a prop to force a blur() when event.key == 'Enter'

This should also either attempt to detect multi-line pastes (which I assume is fraught with cross-browser peril because contentEditable) and designDecision(chop everything but the first line | join the lines), or check for linebreaks in _onInput() and update innerHTML to remove them.

[insin]

This is also potentially breaking if we default to single line and add a multi line boolean prop instead of vice-versa.